The Schlieren-type color television projector, commonly referred to as a light valve projector, was first developed over ten years ago and has been used extensively for large screen visual displays in many applications, including flight simulators. The light valve essentially utilizes a color filter plate/lens assembly to spatially separate the green/magenta colors from the light produced by a projection lamp. An electron beam deformable control surface generates difraction patterns for color modulation. A Schlieren optical imaging system produces an output comprised of a plurality of spatially separated, converging rays of component colors. With this projection system, significant advantages are obtained including improved resolution, definition, and brightness thereby permitting larger screen color television imaging than was previously possible with other television systems.
As a result of this Schlieren projection lens, the cross section of the light body (bundle) emanating from the lens contains spatially separated green/magenta color areas that converge and combine correctly to form an image at the focal point of the lens. Attempts to modify the image through the use of optical devices coupled to the Schlieren lens have met with very limited success in that the image degrades rapidly unless all of the output light body is utilized in the projected image. However, with an optical system, such as a zoom lens, or aperture device utilizing an iris, a portion of the output is either masked or vignetted such that it will not be transmitted through the optical array. When all of the light body is not transmitted, color balance deteriorates rapidly, or undesirable color fringing, or even complete degradation of the final projected image occurs. This limitation of the Schlieren light valve dramatically reduces its utility in such applications as a flight simulator as the projected image in a simulator must be capable of quick and accurate changes in magnification, focus, and image brightness which is typically achieved through a conventional optical device which would degrade the Schlieren image. Furthermore, previous Schlieren light valves did not utilize conventional zoom lenses or other such optical devices because of their variable aperturing of the light body.
To solve the problems of the prior art which limited the applicability and usefulness of the Schlieren light valve in those applications such as a flight simulator, the inventors herein have developed a technique for translating the output of the Schlieren light valve into a light body which can be passed through conventional optical devices such as zoom lenses and the like which utilize aperture control and which do not degrade the final projected image. This technique consists essentially of focusing an image made visible by the Schlieren optical system onto an intermediate surface, such as a fiber optic rear projection screen (FORPS), which collects and redistributes the color information emanating from the light valve from the spatially separate converging rays of green/magenta colors into an image plane comprised of spatially combined diverging rays of combined colors. The fiber optic rear projection screen (FORPS) can be made of virtually any fiber optic material of any thickness or length, with any numerical aperture, have ground or polished surfaces, and even contain impurities, kinks, bias cuts or tapers. The inventors herein have tested FORPS having thickness of 0.06 inches to 0.2 inches and they have successfully translated the Schlieren light body. The thicker FORPS have a tendency to increase the mixing of the light body and thus be less susceptible to degradation of the image as it is passed through conventional optics while thinner FORPS have the advantage of transmitting more light and are thus more efficient.
In a preferred embodiment of a projector as utilized in a flight simulator, a decollimating lens is inserted in front of the light valve along its optical axis to focus the light at an intermediate plane. At the focal point, a rigid FORPS containing a plurality of fibers arranged in coherent fashion and parallel to the optical axis is located and the image appears thereon. Due to the nature of the FORPS, the image is transmitted through the FORPS and out the back surface. The image transmitted through the surface and emanating therefrom is used as the source for a projection lens which further processes the image, as desired. This conventional optical projection lens can be apertured by an iris, or controlled by vignetting when a zoom-type projection lens is used, without undesirable spectral affects at the final projected image as would otherwise be experienced with the Schlieren light valve output.
The foregoing has been a brief description of the principal advantages and features of the present invention. A more thorough understanding thereof may be attained by referring to the drawings and description of the preferred embodiment which follows.